Formation treating for purposes of sand consolidation, water exclusion or well plugging for abandonment are well known terms applying to procedures routinely practiced in the commercial production of petroleum. When wells are completed in petroleum-containing formations which also contain unconsolidated granular mineral material such as sand or gravel, production of fluids from the formation causes the flow of the particulate matter, e.g. sand, into the wellbore, which often leads to any of several difficult and expensive problems. Sometimes a well will "sand up", meaning the lower portion of the production well becomes filled with sand, after which further production of fluid from the formation becomes difficult or impossible. In other instances, sand production along with the fluid results in passage of granular mineral material into the pump and associated hardware of the producing well, which causes accelerated wear of the mechanical components of the producing oil well. Sustained production of sand sometimes forms a cavity in the formation which collapses and destroys the well. All of these problems are known to exist and many methods have been disclosed in the prior art and applied in oil fields in order to reduce or eliminate production of unconsolidated sand from a petroleum formation during the course of oil production.
Another problem encountered in oil production to which the present process offers an attractive solution is encountered when a well is in fluid communication with a section that includes one or more oil producing intervals and one or more water producing intervals. Production from such a zone results in production of some oil and some water. Since the viscosity of water is less than the viscosity of oil, a much larger volume of water than oil is frequently produced. There are many prior art processes for controlling fluid entry into wells, but none are entirely satisfactory.
Another problem that is frequently encountered in commercial petroleum production operations arises when it is desired to completely plug a well which is to be abandoned. The long term durability of the material used to plug wells for abandonment is of high current interest because of the danger that salt water or petroleum might enter and contaminate fresh water-containing intervals, or otherwise damage the environment.
The above-described production problems and potential solutions to the problems have been the subject of extensive research by the petroleum industry. One general approach suggested in the prior art for consolidating sand to form a fluid permeable zone around the well involves consolidating the porous but unconsolidated sand structure around the wellbore in order to cement the loose sand grains together, thereby forming a permeable mass which will allow production of fluids from the formation into the well but which will restrain the movement of sand particles into the wellbore. Another approach involves removing a portion of the formation around the well and packing specially prepared granular material into the formation around the wellbore which is subsequently caused to be cemented together in a manner which maintains fluid permeability.
It is a primary objective of any successful sand consolidation method that a barrier be formed around the wellbore which restrains the movement of sand particles into the well while offering little or no restriction to the flow of fluids, particularly oil, from the formation into the wellbore where it can be pumped to the surface of the earth. Consolidation only needs to extend into the formation to a depth of 6 to 12 inches around the periphery of the perforations or other openings in the outer casing of the production well.
The objective of a water exclusion of fluid entry control process is to form an impermeable barrier around the well to prevent the flow of sand and formation fluids into the well. A process similar to that used to control sand problems can be used for plugging formation for water exclusion, provided the process is modified to cause creation of an impermeable barrier rather than a permeable barrier.
A very important quality of a satisfactory sand consolidation method, plugging or water exclusion method is durability of the permeable or impermeable barrier formed around the wellbore. Once a permeable barrier for sand control is formed and the well is placed on production, there will be a continuing flow of fluids through the flow channels within the permeable barrier, and it is important that the barrier last for a significant period of time, e.g. several months and preferably years, without excessive abrasive wear or other deterioration of the consolidation matrix which would cause the particulate matter to flow once again into the wellbore. Similarly, it is important that impermeable barriers formed for fluid entry control, or for preparing a well for abandonment, be long lasting.
It is also important that the material injected into the formation for all of our formation treating methods described above should be essentially unreactive during the period it is inside the wellbore, i.e. while it is being pumped down the well and positioned where it is desired adjacent to the perforations of the production casing.
The processes employing the furfuryl alcohol oligomer or monomer have been used with consistently high success rates in many field applications. It has been noted, however, that the fluid density of the treating fluid, which is about 9.75 pounds per gallon, makes the process difficult to apply when the formation fluid density is equal to or greater than 9.75 pounds per gallon. There is, therefore, an unsatisfied need for a treating fluid and process which can be used to treat formations containing fluids greater than 9.75 pounds per gallon.